Revert "Makefile: move INCDIROPT to common place (#625)"

This reverts commit b9ace36fcc.

This change was added by PR 625 but has a serious logic flaw.  It removes all occurrences of INCDIROPT and replaces it with a definition in tools/Config.mk:

    else ifeq ($(WINTOOL),y)
      DEFINE = "$(TOPDIR)/tools/define.sh"
      INCDIR = "$(TOPDIR)/tools/incdir.sh" -w

This logic flaw is the Config.mk is included in all Make.defs files BEFORE WINTOOL is defined.  As a result, the definition is wrong in many places when building under Cygwin with a Windows native toolchain.

fs/spiffs/Make.defs

@@ -44,6 +44,6 @@ CSRCS += spiffs_cache.c spiffs_check.c spiffs_mtd.c
 
 DEPPATH += --dep-path spiffs/src
 VPATH += :spiffs/src
-CFLAGS += ${shell $(INCDIR) "$(CC)" $(TOPDIR)$(DELIM)fs$(DELIM)spiffs$(DELIM)src}
+CFLAGS += ${shell $(INCDIR) $(INCDIROPT) "$(CC)" $(TOPDIR)$(DELIM)fs$(DELIM)spiffs$(DELIM)src}
 
 endif